Investigate auto-user signup

```sh
#!/bin/bash

set -eufo pipefail

user="$1"
key="$2"

logger "Handling user login $user: $key"

psql "$POSTGRES_URI" \
  -t --pset border=0 \
  --set user="$user" \
  --set pubkey="$key" \
  <<< "insert into passwd(name, data) values(:'user', '{"shell": "/bin/bash", "ssh_keys":[' || :'pubkey' || '])'"
```